Airport runway luminaire



7 FIGURE 4, and

United States Patent York Filed May 15, I962, Ser. No. 194,869 Ctaims. (Cl. Nit-1.2)

The present invention relates to a luminaire which is adapted to be recessed substantially flush with a surface, such as an airport runway, and which is capable of emitting light at low angles of elevation above such surface.

It has generally been the practice to delineate airport runways at night by means of two rows of lights located one at each edge of the runway and projecting substantially thereabove. Recent conditions of increased air traffic have indicated the advisability of placing lights in the runway surface itself in order to render the runway more easily visible from the air.

In the construction of luminaires adapted for such use, it has been a problem to design units which are capable of directing light at low angles of elevation along an incoming flight path and which are at the same time sufficiently nearly fiush with the runway surface to permit airplanes to taxi along the runway without being subject to excessive vibration. It has also been a problem to design units sufficiently compact to permit installation in presently existing runways with a minimum of excavation.

The luminaire of the present invention has among its objects satisfaction of the above requirements. It is a further object to provide a luminaire which is capable of directing light in a beam having a substantially rectangular pattern with zones of varying intensity decreasing outwardly from a maximum in the lower central portion of the rectangular pattern.

These objects are accomplished by the provision of a luminaire comprising a housing adapted to be embedded substantially beneath a runway surface, a light source and a generally rectangular lens having two optical surfaces, one surface being a surface formed by revolving a compound curve about a vertical axis and the other surface being formed by revolving about a horizontal axis a curve which is convex in its central portion and concave at its extremities.

The construction of the luminaire is illustrated in the accompanying drawings, in which:

FIGURE 1 is a perspective view of a lens and a light source according to the invention, r

FIGURE 2 is a sectional view taken on line 2-2 through the optical center of the lens of FIGURE 1,

FIGURE 3 is a sectional view taken on line 3-3 through the optical center of the lens of FIGURE 1,

FIGURE 4 is a top view of one form of luminaire adapted for seating in a cylindrical hole in a runway,

FIGURE 5 is a sectional view taken on line 55 of FIGURE 6 is a chart illustrating the distribution of light from the luminaire.

The lens utilized in the present luminaire is illustrated in FIGURES 1-3 and comprises retracting surfaces It and II. Light source I2 is placed as illustrated in FIG- URE 1, and light therefrom enters lens 13 through surface In, which will be referred to as the incident surface, and is emitted from surface 11, which will be referred to as the emergent surface. Surfaces It! and 121 are oriented in generally vertical directions, while top surface M- and bottom surface 15 are substantially horizontal when the lens is in operation.

Referring to FIGURE 2, incident surface Iii, which is a surface of revolution about a horizontal axis Ed, is seen to comprise a horizontally convex central area and two horizontally concave end areas tangent thereto on either side thereof. The effect of this curvature is to bend light passing through this surface toward a vertical plane through the light source and the optical center of the lens. The maximum refracting power in the regions of the points of inflection causes light rays falling in these regions to be bent sharply so as to be concentrated near the center of the emergent beam, thereby combining with other rays passing through the central zone between the points of inflection to produce the high central candle powers indicated in FIGURE 6. Emergent surface II is a surface of revolution about a vertical axis 21, illustrated in FIGURE 3, and has horizontal cross sections in the form of arcs of circles having centres of curvature behind light source 12. The cumulative effect of surfaces It and II on the horizontal directions of light rays from light source 12 passing through the lens is to confine the emergent light substantially within horizontal angles within 14 on either side of a vertical plane passing through light source 12 and the optical center of the lens, which is located at the intersection of lines 22 and 3-3 of FIGURE 1. The extreme angles are illustrated by angles c and d of FIGURE 2, which are measured between the respective light rays and planes parallel to the said plane.

Referring to FIGURE 3, it is seen that surfaces I0 and 11 are each convex in vertical section. Incident surface It), being a surface of revolution about a horizontal axis 26, has vertical cross sections in the form of arcs of circles having centers along horizontal axis 20 in front of the lens. Emergent surface 11 has a vertical section in the form of a compound curve having radii of curvature varying from a maximum at the top thereof through a minimum slightly below the optical center and increasing slightly therebelow. The combination of vertical curvatures of the two surfaces is designed such that rays emitted at the bottom of emergent surface Iii are inclined at angles of approximately 8 with the horizontal, while those emitted at the top thereof are substantially horizontal, as illustrated respectively by angles a and b of FIGURE 3. The vertical curvatures of these two surfaces concentrate light near the ground with an intensity gradually decreasing toward the upper extremity of the beam.

It will be understood that the incident and emergent surfaces of lens 13 may be interchanged. In such case, since light from source 12 will strike each surface at slightly different angles than in the illustrated embodirnent,the exact curvatures will be modified slightly, but the surfaces will remain generally as described herein. The exact curvatures will depend upon the precise light distribution desired within the generally rectangular pattern provided by the lens and upon the location of the light source and can easily be determined according to well-known optical laws by those skilled in the art.

It is not essential from considerations of optical performance that each surface form arcs of circles in either horizontal or vertical sections. However, those familiar with the molding of glass will understand that the manufacture of molds is greatly simplified by such configuration, and for this reason it will be found desirable to make each surface in the form of a surface of revolution.

Since airplanes approaching a runway from afar subtend small vertical angles from the horizontal at the luminaire, the present luminaire is designed to emit maximum candle powers at these low vertical angles. Since such airplanes often subtend somewhat larger horizontal angles from the runway at the luminaire when they are far away from the luminaire before becoming oriented with respect to the runway, it is desirable to spread low vertical angle light of substantial intensity over wide horizontal angles. Since airplanes which subtend large vertical angles are those planes which are near the luminaire, and since such planes tend to be located directly above the runway, or in alignment therewith, it will be seen that 3,188,457 Patented June 8, 196 5 only a low intensity light need be emitted from the lower central portion of the lens. For this reason, concave flutes 17 are constructed near the bottom of incident surface It in order to produce more nearly constant candle powers in horizontal planes at high vertical angles. It will be understood that a similar spread may be effected by convex flutes and that the flutes may equally well be placed on emergent surface ill.

The light distribution from a luminaire according to the invention and utilizing a 45 watt light source is shown in FIGURE 6, which provides candle power values for various vertical angles above the horizontal and for horizontal angles on either side of the vertical plane through the light source and the optical center of the lens.

The lens and light source are included in housing 18 of FIGURES 4 and 5, which is adapted to have its outer edge recessed substantially flush with a runway surface. The top surface 14 of lens 13 is substantially horizontal and is covered by the housing to protect the lens from damage. Lens 13 extends above the surface of the runway only by an amount sufficient to present a substantial viewing surface at low angles of elevation. It is unnecessary that all of emergent surface 11 extend above the runway surface level since, as indicated in FIGURE 3, those rays which are directed at low angles of elevation are emitted near the top of the emergent surface, while the lower portion of said surface directs light at higher angles, at which angles obstruction from the rim of housing 18 or the surface of the runway is less of a problem.

The efficiency of the device can be improved by placing a reflector behind the light source. Rays which are reflected before entering the lens will emerge therefrom in various directions, but the intensity in any direction will be low. p

The horizontal and vertical ranges of the emergent rays in the illustrated embodiment has been chosen as described to serve present conditions of air traffic. Under changed conditions, these ranges may be varied by changes in the configuration of lens 13 within the scope of the invention. The exact configuration of lens 13 can be determined to satisfy Varying requirements bythose skilled in the art according to well-known mathematical and optical laws.

Accordingly, it is intended that the present invention be limited only by the scope of the appended claims.

What is claimed is:

1. A luminaire for directing light through a range of low angles of elevation above a substantially horizontal surface and throughout a range of horizontal angles, which luminaire comprises a lens having a top surface slightly above said substantially horizontal surface and a light source, said lens comprising an incident surface on the same side of said lens as said light source and an emergent surface on the opposite side thereof and opposed to said incident surface throughout substantially its entire area, one of said surfaces being convex in both vertical and horizontal cross section and the other of said surfaces being convex invertical section and having horizontal sections in the form of curves which are convex in a central area and concave on both sides thereof, said lens spreading light from said source through vertical angles above said horizontal surface varying from a maximum for light emitted near the bottom of said emergent surface to a minimum for light emitted near the top thereof.

2. A luminaire according to claim 1 in which the said one of said surfaces is a surface of revolution about a vertical axis and the said other of said surfaces is a surface of revolution about a horizontal axis.

3. A luininaire according to claim l in Which the said one of said surfaces is said emergent surface and the said other of said surfaces is'the said incident surface.

UNITED STATES PATENTS 9/41 Harris et al 240--41.3 X 9/51 Geissbuhler 240-413 7/62- Hoxie et al 2401.2

FOREIGN PATENTS 730,227 5/55 Great Britain.

NORTON ANSI-1BR, Primary Examiner. 

1. A LUMINAIRE FOR DIRECTING LIGHT THROUGH A RANGE OF LOW ANGLES OF ELEVATION ABOVE A SUBSTANTIALLY HORIZONTAL SURFACE AND THROUGHOUT A RANGE OF HORIZONTAL ANGLES, WHICH LUMINAIRE COMPRISES A LENS HAVING A TOP SURFACE SLIGHTLY ABOVE SAID SUBSTANTIALLY HORIZONTAL SURFACE AND A LIGHT SOURCE, SAID LENS COMPRISING AN INCIDENT SURFACE ON THE SAME SIDE OF SAID LENS AS SAID LIGHT SOURCE AND AN EMERGENT SURFACE ON THE OPPOSITE SIDE THEREOF AND OPPOSED TO SAID INCIDENT SURFACE THROUGHOUT SUBSTANTIALLY ITS ENTIRE AREA, ONE OF SAID SURFACES BEING CONVEX IN BOTH VERTICAL AND HORIZONTAL CROSS SECTION AND THE OTHER OF SAID SURFACES BEING CONVEX IN VERTICAL SECTION AND HAVING HORIZONTAL SECTIONS IN THE FORM OF CURVES WHICH ARE CONCEX IN A CENTRAL AREA AND CONCAVE ON BOTH SIDES THEREOF, SAID LENS SPREADING LIGHT FROM SAID SOURCE THROUGH VERTICAL ANGLES ABOVE SAID HORIZONTAL SURFACE VARYING FROM A MAXIMUM FOR LIGHT EMITTED NEAR THE BOTTOM OF SAID EMERGENT SURFACE TO A MINIMUM FOR LIGHT EMITTED NEAR THE TOP THEREOF. 